High-frequency induction heating apparatus



July 26, 1949. R. .1. DETUNO HIGH-FREQUENCY INDUCTION HEATING APPARATUS Filed Sept. 28, i945 Patented July 26, 1949 HIGH-FREQUENCY INDUCTION HEATING APPARATUS Rocco J. Detuno, Chicago, Ill., assignor to, Western Electric Company Incorporated, New York, N. Y., a corporation of New York.

Application September 28, 1945, Serial'No. 619,129

5. Claims. (Cl. 21S-47) This invention relates to heating apparatusand more particularly to electrical high frequency induction heating apparatus.

In many instances where, circular or annular objects are heated by electrical induction heating, multi-turn coils cannot be used for one reason or another, depending upon the particular circumstances. Where multi-turn coils have not been practicable, single-turn coils have been used. However, a serious problem presents itself when heating circular objects with a conventional single-turn coil to obtain uniformY heating throughout a 360 area of revolution. Practical experience has shown that there is always a cold spot in the area adjacent to the. space between the ends of the single-turn coil.

An object o f the present invention is to provide a single-turn induction heating coil which will urnish uniform heating throughout a full 360 urn.

In accordance with one embodiment of the invention, a single-turn induction heating coil is provided with leads which, at the point of their attachment to the ends of the coil, are substantially narrower in cross section than the width of the conductor forming the turn of the coil in order to provide a stronger high frequency eld at the ends of the coil, thereby maintaining a more uniform eld throughout the 360 degrees of the coil turn.

A complete understanding of the invention may be had by reference to the following detailed description taken in conjunction with the accompanying drawings, in which Fig. 1 is a plan View of an induction heating coil embodying the features of the invention;

Fig. 2 is a side elevation partly in section of the apparatus illustrated in Fig. 1, showing its relationship to an object being heated;

Fig. 3 is a vertical section of the apparatus taken on the line 3-3 of Fig. 1; and

Fig. 4 is a vertical section of the apparatus taken on the line 4-4 of Fig. 1 showing the joint between a lead and the coil and indicating the path of part of the high frequency field.

Referring to the drawings, it will be seen that the apparatus is provided with a single-turn coil I 5l formed from a conductor il having a rectangular cross section and provided with a cooling duct l2 which extends through the turn of the coil. The coil Ill is electrically connected to a source of high frequency current I3 through a pair of leads i4 and Iii each having one end connected to the coil I 0. At the opposite end, the leads are provided with a pair of substantially U-shaped terminals and 2i which are secured to, the terminals I6 of the source of high frequency current I3. The leads I4 and I5 are se.- cured to the ends of. the coil I0 normal to the planev of the` coil and extend upward to a point I1', thence at a convenient angle to the terminals t6 of the source of high frequency current I3. Each of the leads is provided with a passage 22 which connects at one end tothe cooling duct of the coi-l and at the other end to a pipe line 23 containing a circulating liquid coolant. The cross section of the leads I4 and I5, at their points of attachment to the coil I0, is narrower than the width of the conductor I I. It is important that at the point of attachment to thel coil, the outer surfaces of the leads be between and substantially spaced from opposite sides of the conductor Il which in this embodiment are the inner and outer peripheral edges of the coil I0.

Fig. 2 illustrates one application of the invention, An annular flange 24, which is to be brazed to a cylindrical pipe 25, is shown being carried on a movable article holding table 3U which is more fully described in the copending application of J. R. Johnson, Serial No. 626,561, filed November 3, 1945. The table 30 is provided with apertures 3l and 32 to freely accommodate a pair of studs 33 and 34 which are to be brazed to the flange 24. It is apparent that in order to provide brazing heat at the studs and at the juncture of the pipe 25 and the flange 24 simultaneously, the high frequency field must affect -a greater area in the plane of the ange 24. This is accomplished by making the width of the conductor II greater than its height (Fig. 2) thus providing a longer path for the field along the area of the flange 24.

It has been found that the cold spot which ordinarily exists between the ends of single-turn induction heating coils is for all practical purposes eliminated by the invention herein. Although the explanation for this phenomenon is not clearly known, it is believed that the formation of a cold spot between the ends of the coil is prevented by the use of leads I4 and I5 which are smaller in cross section than the width of the conductor II at their point of attachment to their conductor, thus providing a greater unimpeded path 35 (Fig. 4) for lines of force in the immediate vicinity of the ends of the coil.

What is claimed is:

1. In an electrical induction heating apparatus, a source of high frequency current, a singleturn coil formed from a hollow electrical conductor, said coil having adjacent ends within the outer peripheral boundary of the coil turn, and a pair of hollow electrical leads connected to the ends of said coil at right angles to the plane of said coil, said leads having a narrower cross section than the width of said conductor at the point of said connection to said coil, and the outer surfaces of said leads at the point of connection to said coil being between and spaced from the inner and outer peripheral boundaries of said coil.

2. An electrical induction heating apparatus comprising a single-turn coil for-med from an electrical conductor, said coil having adjacent ends within the outer peripheralboundary of the coil turn, and a pair of electrical leadsconnected to the ends of said coil at right angles to the plane of said coil, said leads having a narrower cross section than the width of said conductor at the point of said connection to said coil, and the outer surfaces of said leads at thepoint of connection to the coil -being between Iand spaced from the inner and outer peripheral boundaries of the coil turn.

' 3. An electrical induction heating apparatus comprising a single-turn coil formed from an electrical conductor, said coil having adjacent er1-ds within the peripheral boundary of the coil turn, and a pair of electrical leads connected to the ends of said coil and at an angle to the plane of said coil, said leads having a narrower cross section than the portion of the conductor at the point of said connection to said coil, and the outer surfacesrof said leads at the point of connection to the coil being between and spaced from opposite boundaries of said conductor.

4. An electrical induction apparatus comprising'ra single-turn coil formed from an electrical conductor, said coil having adjacent ends within the outer peripheral boundary of the coil turn, and a pair of electrical leads connected to the ends of said coil and on the face of the con- 4 ductor opposite to the face of the conductor adjacent the desired heating area, said leads having a narrower cross section than the width of said conductor at the point of said connection to said coil, and the outer surfaces of said leads at the point of connection to the coil being between and spaced from opposite boundaries of said conductor. A

5. An electrical induction heating apparatus comprising a single-turn coil having adjacent ends Within the outer peripheral boundary of thecoil turn and being formed from an electrical conductor having an oblong cross section to providev a greater heating area, and a pair of electrical leads connected to the ends of said coil at right angles to the plane of said coil and on the face of the conductor opposite the face of the conductor adjacent the area of desired maximum heating, said leads having a narrower cross section than the Width of said conductor at the point of said connection to said coil, and the outer surfaces of said leads being between and spaced from the inner and outer peripheral boundaries of the coil turn.

' ROCCO J. DETUNO.

REFERENCES CITED The following references are of record in the le of this. patent:

UNITED STATES PATENTS Number Name Date 2,321,189 Dravneek June 8, 1943 2,353,130 Dravneek July 1l, 1944 2,394,944 Stanton Feb. l2, 1946 2,397,990 Sherman Apr. 9, 1946 2,402,508 `Strickland June 18, 1946 2,414,141 Denneen et al. Jan. 14, 1947 

